1. Field of the Invention
The present invention relates to a method and apparatus for the continuous measurement of the caloric value of a combustible gas.
More specifically, the caloric value or heating power of a gas is measured by a calorimeter having a central chimney housing a burner, a means for supplying the combustible gas at a given pressure and flow rate, and two annular concentric cells. The external wall of the external cell is provided a heat exchanger for regulating its temperature. The concentric cells are separated by an annular dividing wall parallel to the cell of walls and are connected to a differential pressure sensor.
2. Description of the Related Art
A calorimeter of this general type is disclosed in French patent application No. 81 18722, published Apr. 5, 1983 (corresponding to U.S. Pat. No. 4,500,214) in the joint name of Onera and the present inventor. In this calorimeter, the internal and external cells have small thicknesses with respect to their length. Thus, the temperature gradient formed in the cells is substantially normal to the walls. These cells are concentric and annular. Convection currents are practically nonexistent and the heat flow passes through the calorimeter in a substantially radial direction without being disturbed by upward and downward movements of convection.
Measurement of the thermal flow is made by a different gas thermometer. Two cells are filled with the same gas and separated by a dividing wall having a certain thermal resistance. Heat passes radially through the wall inducing a temperature rise in the cells. The difference of the voluminal integral of the temperatures in each cell is proportional to the heat flow released by the combustion of a combistive gas. Thus, the difference of the pressure existing in each cell is proportional to the flow according to the following formula: EQU .DELTA.P=K.sub.1 .DELTA..theta.=K.sub.2 .PSI.
where:
.DELTA..theta. is the mean temperature difference in the cells; and, PA1 .omega. is the heat flow due to the combustive gas. PA1 q.sub.g is the flow rate of the combustible gas; and,
However, when measuring the heat content of a gas, care must be taken that the calorimeter measures only the latent condensation heat of the water formed by combustion of the gas. The prior art obtains incorrect readings because of the latent condensation of water contained in the initial combustive air. Also, the non-condensation of a part of the water formed by combustion and the non-saturation of the combustion air produces inaccurate readings.
In the present invention, we assume: EQU .DELTA.P=K.sub.3 .multidot.q.sub.g .multidot.PCS.sub.g
where:
PCS.sub.g is the heat content of the gas.